When Is the Last Frost in Iowa?
The average last spring frost in Iowa falls between April 19 and May 3 for most ZIP codes, with a statewide median of April 28. At the average date a later frost is still a coin flip, so tender plants wait for the safer 90% date.
| City | Last frost | 90% safe after | First frost | Growing season |
|---|---|---|---|---|
| Des Moines | Apr 18 | May 2 | Oct 20 | 184 days |
| Cedar Rapids | Apr 28 | May 13 | Oct 12 | 166 days |
| Davenport | Apr 23 | May 8 | Oct 15 | 174 days |
| Sioux City | Apr 29 | May 11 | Oct 7 | 161 days |
| Ankeny | Apr 23 | May 6 | Oct 15 | 173 days |
| Iowa City | Apr 21 | May 6 | Oct 18 | 180 days |
| West Des Moines | Apr 18 | May 2 | Oct 20 | 184 days |
| Ames | Apr 26 | May 9 | Oct 8 | 164 days |
| Waterloo | Apr 27 | May 10 | Oct 10 | 165 days |
| Council Bluffs | Apr 18 | Apr 30 | Oct 21 | 185 days |
| Dubuque | Apr 19 | May 4 | Oct 21 | 184 days |
| Marshalltown | Apr 28 | May 11 | Oct 7 | 162 days |
| Mason City | Apr 29 | May 9 | Oct 7 | 161 days |
| Ottumwa | Apr 23 | May 7 | Oct 14 | 172 days |
| Fort Dodge | Apr 28 | May 9 | Oct 8 | 162 days |
| Clinton | Apr 13 | Apr 28 | Oct 26 | 195 days |
| Burlington | Apr 15 | May 1 | Oct 20 | 187 days |
| Muscatine | Apr 24 | May 9 | Oct 14 | 172 days |
Last and first frost: 50% (median) dates of the last spring and first fall 32 °F night. 90% safe after: only a 10% chance of a later spring frost. First frost dates in January fall in the following winter. Each city uses the NOAA station nearest the ZIP code closest to its center.
Across all 150 Iowa weather stations with frost records, median last frost dates run from April 10 at Keokuk Lock Dam 19, IA to May 8 at Cresco 1 NE, IA. Elevation, valleys that collect cold air and distance from large water bodies explain most of the spread, so a garden a few miles from a listed city can differ by a week or more. The ZIP code lookup above uses the same NOAA data as the frost date calculator for every US ZIP code.
When Is the First Frost in Iowa?
The average first fall frost in Iowa arrives between October 3 and October 19 for most ZIP codes, with a median of October 10. Tomatoes, peppers, basil and squash are damaged at 32 °F, so harvest or cover them before then.
Fall frost can come early: Des Moines has a 10% chance of frost before October 4, Cedar Rapids has a 10% chance of frost before September 29 and Davenport has a 10% chance of frost before October 1. Hardy crops such as kale, spinach and cabbage tolerate light frosts and keep producing after the first frost date.
When to Plant Tomatoes in Iowa?
Transplant tomatoes in Iowa 1 to 2 weeks after the local average last frost, once nights stay above about 50 °F: Apr 25 – May 2 in Des Moines, May 5 – May 12 in Cedar Rapids and Apr 30 – May 7 in Davenport. Start seeds indoors 6 to 8 weeks before the last frost.
| City | Start seeds indoors | Transplant outdoors | Lowest-risk transplant |
|---|---|---|---|
| Des Moines | Feb 21 – Mar 7 | Apr 25 – May 2 | after May 2 |
| Cedar Rapids | Mar 3 – Mar 17 | May 5 – May 12 | after May 13 |
| Davenport | Feb 26 – Mar 12 | Apr 30 – May 7 | after May 8 |
| Sioux City | Mar 4 – Mar 18 | May 6 – May 13 | after May 11 |
| Ankeny | Feb 26 – Mar 12 | Apr 30 – May 7 | after May 6 |
| Iowa City | Feb 24 – Mar 10 | Apr 28 – May 5 | after May 6 |
| West Des Moines | Feb 21 – Mar 7 | Apr 25 – May 2 | after May 2 |
| Ames | Mar 1 – Mar 15 | May 3 – May 10 | after May 9 |
| Waterloo | Mar 2 – Mar 16 | May 4 – May 11 | after May 10 |
| Council Bluffs | Feb 21 – Mar 7 | Apr 25 – May 2 | after Apr 30 |
| Dubuque | Feb 22 – Mar 8 | Apr 26 – May 3 | after May 4 |
| Marshalltown | Mar 3 – Mar 17 | May 5 – May 12 | after May 11 |
| Mason City | Mar 4 – Mar 18 | May 6 – May 13 | after May 9 |
| Ottumwa | Feb 26 – Mar 12 | Apr 30 – May 7 | after May 7 |
| Fort Dodge | Mar 3 – Mar 17 | May 5 – May 12 | after May 9 |
| Clinton | Feb 16 – Mar 2 | Apr 20 – Apr 27 | after Apr 28 |
| Burlington | Feb 18 – Mar 4 | Apr 22 – Apr 29 | after May 1 |
| Muscatine | Feb 27 – Mar 13 | May 1 – May 8 | after May 9 |
Indoors: 6–8 weeks before the average last frost. Outdoors: 1–2 weeks after it. Lowest-risk: after the date with only a 10% chance of a later frost. Rules of thumb; check the 10-day forecast and wait for soil near 60 °F.
Tomatoes stall below about 50 °F at night and are killed by frost, so a week or two of waiting after the average date costs little. The tomato plant care guide covers light, watering and feeding once plants are in the ground.
What Can You Plant in Des Moines and When?
Des Moines's average last frost of April 18 anchors its spring planting calendar: peas and spinach go in from March 7, broccoli and lettuce transplants from March 21, and tomatoes, peppers and squash after April 25.
| Crop | Start seeds indoors | Plant outdoors | Frost tolerance |
|---|---|---|---|
| Peas | — | Mar 7 – Mar 21direct sow, 4–6 weeks before last frost | hardy |
| Spinach | — | Mar 7 – Mar 28direct sow, 3–6 weeks before last frost | hardy |
| Radishes | — | Mar 14 – Mar 28direct sow, 3–5 weeks before last frost | hardy |
| Onions (sets) | — | Mar 21 – Apr 4plant, 2–4 weeks before last frost | hardy |
| Potatoes | — | Mar 21 – Apr 4plant, 2–4 weeks before last frost | half-hardy |
| Broccoli & cabbage | Feb 21 – Mar 7 | Mar 21 – Apr 4transplant, 2–4 weeks before last frost | hardy |
| Lettuce | Mar 7 – Mar 21 | Mar 21 – Apr 4transplant, 2–4 weeks before last frost | hardy |
| Beets | — | Mar 21 – Apr 4direct sow, 2–4 weeks before last frost | half-hardy |
| Carrots | — | Mar 28 – Apr 4direct sow, 2–3 weeks before last frost | half-hardy |
| Tomatoes | Feb 21 – Mar 7 | Apr 25 – May 2transplant, 1–2 weeks after last frost | tender |
| Basil | Feb 21 – Mar 7 | Apr 25 – May 9transplant, 1–3 weeks after last frost | tender |
| Peppers | Feb 7 – Feb 21 | May 2 – May 9transplant, 2–3 weeks after last frost | tender |
| Eggplant | Feb 7 – Feb 21 | May 2 – May 9transplant, 2–3 weeks after last frost | tender |
| Green beans | — | Apr 25 – May 9direct sow, 1–3 weeks after last frost | tender |
| Sweet corn | — | Apr 25 – May 9direct sow, 1–3 weeks after last frost | tender |
| Cucumbers | Mar 21 – Mar 28 | Apr 25 – May 9transplant, 1–3 weeks after last frost | tender |
| Squash & zucchini | Mar 21 – Mar 28 | Apr 25 – May 9transplant, 1–3 weeks after last frost | tender |
| Watermelon | Mar 21 – Mar 28 | May 2 – May 9transplant, 2–3 weeks after last frost | tender |
Dates for Des Moines (last frost Apr 18, NOAA station Des Moines INTL AP, IA, 4 miles from ZIP 50309). General rules of thumb; wait for soil near 50 °F for most seeds and 60 °F for beans, corn and squash.
How Long Is the Growing Season in Iowa?
The frost-free growing season in Iowa lasts about 153 to 180 days for most ZIP codes, with a median of 165 days. Among the listed cities, Sioux City has the shortest season at 161 days and Clinton the longest at 195.
Season length decides which varieties ripen: compare it with the “days to maturity” on seed packets, counted from transplanting for tomatoes and peppers. NOAA stations in Iowa range from 145 days at Sheldon, IA to 198 days at Keokuk Lock Dam 19, IA. Planning beds before the season starts helps in short seasons — a plant spacing calculator for vegetable beds shows how many transplants fit.
What Hardiness Zones Are in Iowa?
Iowa spans USDA hardiness zones 4b to 6a, with zone 5a the most common. Zones describe winter cold and decide which perennials survive, while frost dates set when to plant annual vegetables and flowers.
The Iowa planting zone map with the zone of each city shows how the zones are spread across the state and which plants are hardy in all of them.
Frequently Asked Questions
- When is the last frost in Iowa?
- The average last spring frost in Iowa falls between April 19 and May 3 for most ZIP codes, with a statewide median of April 28. Among major cities it ranges from April 13 in Clinton to April 29 in Mason City.
- When is the last frost in Des Moines, Iowa?
- Des Moines's average last spring frost is April 18, and by May 2 the chance of a later frost drops to 10%. Its first fall frost averages October 20, giving a 184-day growing season (NOAA station Des Moines INTL AP, IA).
- When should you plant tomatoes in Iowa?
- Transplant tomatoes in Iowa 1 to 2 weeks after the local average last frost, once nights stay above about 50 °F: Apr 25 – May 2 in Des Moines, May 5 – May 12 in Cedar Rapids and Apr 30 – May 7 in Davenport. Start seeds indoors 6 to 8 weeks before the last frost.
- When is the first frost in Iowa?
- The average first fall frost in Iowa arrives between October 3 and October 19 for most ZIP codes, with a median of October 10. Harvest tender crops such as tomatoes, peppers and basil before then or cover them on cold nights.
- How long is the growing season in Iowa?
- The frost-free growing season in Iowa lasts about 153 to 180 days for most ZIP codes, with a median of 165 days, from 161 days in Sioux City to 195 days in Clinton.
Frost data: NOAA National Centers for Environmental Information, 1991–2020 U.S. Climate Normals (32 °F freeze dates by probability). ZIP code and city locations and populations: U.S. Census Bureau Gazetteer files and Vintage 2024 population estimates. Planting windows are general rules of thumb. PlantoScan is not affiliated with or endorsed by these agencies.